This invention relates to a method of smelting aluminum by using a blast furnace, and more particularly to a method of smelting aluminum, which permits suppressing the occurrence of a volatile aluminum component and a volatile silicon component, whereby the blocking of the blast furnace can be prevented and the yield of aluminum can be improved.
The aluminum is the most important fundamental metal material next to iron, and the demand therefor is increasing year by year at a high rate. However, the cost of energy has been increased on a worldwide scale in recent years, so that it has become difficult to manufacture aluminum in an area in which the cost of electric power is high, such as Japan. This is giving rise to very serious troubles in the industrial structure. In addition, it is predicted that the area of places having good conditions for the location of inexpensive hydraulic power stations will decrease on a worldwide scale in the future. Consequently, it is being demanded that an inexpensive, energy-saving method of manufacturing aluminum, an important industrial material, be developed
A Bayer-Hall-Heroult method is a conventional method of manufacturing aluminum, which has been known from of old.
However, this method, in which it takes a long period of time to carry out extraction and crystallization operations in a Bayer step, a step of extracting alumina from bauxite, has a low productivity and causes an increase in the cost of equipment. Furthermore, a Hall-Heroult step, an electrolysis step in the above method, does not have any merits with respect to the scale thereof. This step is also industrially disadvantageous in that it causes an increase in the cost of equipment and requires a large amount of electric power. In addition, the above electrolysis step has already little left to be technically improved. Therefore, it has been demanded that a radically-improved, novel aluminum-smelting method be developed.
In order to eliminate these drawbacks encountered in the Bayer-Hall-Heroult method, many kinds of substitute aluminum-smelting methods including a reduction method using an electric furnace have been studied.
However, none of these methods have been so developed as to permit saving energy and reducing the aluminum manufacturing cost to such an extent that these methods can be used satisfactorily instead of the Bayer-Hall-Heroult method. These substitute methods are disadvantageous in that they require, as in a reduction method using an electric furnace, such an amount of electric power that is equal to or larger than that in the older methods, or in that they require, as in an aluminum chloride electrolysis method, a large amount energy and manufacturing cost in a material pretreating steps therein.
In recent years, a method of smelting aluminum by using a blast furnace, in which method a countercurrent moving bed is used to reduce starting alumina-containing material with a carbon material, has come to be discussed as a method capable of overcoming the problems in the above-mentioned aluminum smelting methods using the electric power. In this method using a blast furnace, a packed layer containing starting alumina-containing material, a fuel, and a carbon material working as a reducing agent is formed in the blast furnace to carry out therein simultaneously a combustion reaction (1) and a reduction reaction (2) of the following formulae. EQU C+1/2O.sub.2 .fwdarw.CO (1) EQU Al.sub.2 O.sub.3 +3C.fwdarw.2Al+3CO (2)
The reduction of aluminum oxide (alumina), which is expressed by the formula (2), is carried out by using as a heat source the heat generated in the combustion of a carbon material with oxygen, which is expressed by the formula (1). The blast furnace in use is of a countercurrent moving bed type, in which an oxygen gas is introduced thereinto from a lower portion of the blast furnace with a reduction product withdrawn from a bottom portion thereof. In accordance with a rate of withdrawal of the reduction product, a starting material is fed into the blast furnace from a top portion thereof. A packed layer as a whole moves downward as it keeps in countercurrent contact with a combustion gas occurring in a lower portion of the blast furnace.
Smelting aluminum by carrying out the above reactions (1) and (2) simultaneously in such a blast furnace has various kinds of technical problems to be solved for improving the economical and operation efficiencies.
Above all, the blocking of a blast furnace and a decrease in the yield of aluminum, which are caused by the generation and condensation of volatile aluminum components (Al.sub.2 O and Al) and a volatile silicon component (SiO), are troublesome problems.
In order to suppress the occurrence of such volatile aluminum components and volatile silicon component, a method of adding an alloy component, such as iron to an alumina-containing starting material to lower a reducing temperature and to alloy a metallic aluminum product, whereby the metallic aluminum product can be stabilized to carry out the production of metallic aluminum advantageously, is usually employed.
However, even such a method has not yet been so developed as to thoroughly prevent the occurrence of volatile aluminum components and a volatile silicon component.